I wish they'd find a way to replace all three of them because I'm tried of hearing all of them. Lawler is obviously the worst, though. He admitted to losing his passion for commentating a long while ago. He probably stays because it's a comfortable job that he's been used to doing for awhile and he only has to work one day out of the week (two when it comes to PPVs), barring any promotion he might have to do for the company. Plus, Vince still likes him for some reason, just like he irrationally hates JR for some reason, too.
I haven't enjoyed Lawler much on commentary since he adopted more of a 'tweener' nature starting around 2005/2006.